The present invention pertains to power control in a mobile telecommunication system and more particularly to power control of the links between the base station and the mobile station.
Mobile telecommunication systems include wireless links between mobile stations, which may be mobile telephones, pagers, computers, etc., and the base station of the mobile telecommunication system. Since these links are wireless, the links are susceptible to noise and interference with other signals. The signals received at the mobile station or received at the base station may “fade”. That is, the data signals received by the mobile station or by the base station may become much more attenuated than the surrounding noise and other interference.
The quality of wireless telecommunications is often measured by the ability of the mobile stations and the base station to receive accurate and clear data. As fading of a signal is detected, the base station or the mobile station of the mobile telecommunication system may increase the transmission power it is using to reach the entity at the other end of the link. Further, if the received data signal is not subject to fading the base station or mobile station may decrease the power with which the data is transmitted to the entity at the other end of the link.
When greater power is used on a particular wireless link, this increase in power increases the interference for the other links connecting other mobile stations to the base station.
In a code division multiple access (CDMA) mobile telecommunication system, power control bits are continuously sent, approximately every 1.25 milliseconds, requesting that the entity on the other end of the link to power up by one step or power down by one step. That is, each mobile station continuously sends power control bits (PCB) to the base station, requesting that the base station transmit with greater power since the data signal is fading.
A frame erasure rate (FER), particularly for the reverse channel, i.e., the channel transmitting from a mobile station to a base station, is expected to be at a frame erasure rate of 1 percent. However, current reverse channel control methodology produces a frame erasure rate closer to 2 percent. Current outer loop power control methods provide for these relatively high frame erasure rates. The outer loop power control adjusts power control signal to interference ratio power thresholds used to distinguish between needing to power up and down the mobile station. Generally, these methods increase the power threshold whenever an erroneous frame is received and reduce the power threshold when a good frame is received. This current methodology does not compensate for large bursts of errors such as is typical under actual conditions. As a result, the frame erasure rate is normally considerably higher than 1 percent.
Accordingly, it would be highly desirable to have a power control method which lowers the frame erasure rate (FER) on both the reverse and forward links of a mobile station.